With the development of portable electronic equipments, battery charging circuits are widely used. With the increasing of functions of the portable electronic equipments, its battery capacity becomes higher and higher in order to guarantee the operation time of the portable electronic equipments. Correspondingly, the charging currents of the batteries also become larger and larger to satisfy the charging time that consumers require. Nevertheless, it's extremely difficult for a battery charging circuit to have both small volume and good thermal performance, or have a large charging current while using an inductance with small volume. Furthermore, to realize the flexible in-out configuration, for instance, to apply the adapters with various standards, a novel battery charging circuit is needed.